Selena Gomez's friend "has faith" she is making good romance decisions.

The 22-year-old singer's relationship with Justin Bieber has been on/off for the last couple of years, although they are recently thought to have reunited again.

Selena and Jamie have known each other for years and co-star in this year's emotional drama Rudderless. Jamie has stuck up for her friend, insisting any personal decisions she makes will be well thought through.

"In terms of her personal decisions, you can't tell someone what to do. They're going to discover that on their own. I have faith that she'll be just fine. I know who she is and she's a really great girl," she told New York Daily News.

Selena's decision to reconnect with Justin has raised eyebrows as he is thought to have gone off the rails of late. He's been involved with the law many times this year, including being placed on probation after pleading no contest to a vandalism charge after he was accused of pelting his neighbour's home with eggs in California.

Selena has also had some problems and checked into rehab for two weeks at the beginning of the year. She wasn't treated for drug addiction but hasn't confirmed why she needed help, with suggestions she might have been struggling to deal with her feelings for Justin.

None of this is a concern for Jamie though, who has known the actress-and-singer since she was about 15.

"She has a good head on her shoulders. She comes from a really good family," she explained.

It's not the first time Jamie has jumped to Selena's defence - last month she slammed the amount of speculation there is about the young star's personal life.

"Yeah, totally, that's a bunch of BS," she told E! News. "I mean, her personal life is her personal life. but she's a good woman and she comes from a really good family."